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Boris Dewitte - One of the best experts on this subject based on the ideXlab platform.

  • Vertical structure variability in a seasonal simulation of a medium-resolution regional Model of the Eastern South Pacific
    Progress in Oceanography, 2008
    Co-Authors: Boris Dewitte, Vincent Echevin, Marcel Ramos, Oscar Pizarro, Yves Dupenhoat
    Abstract:

    0079-6611International audienceA seasonal simulation from a medium-resolution ocean general circulation Mode (OGCM) is used to investigate the vertical structure variability of the Southeast Pacific (SEP). The focus is on the extra-tropical Rossby wave (ETRW) variability and associated forcing mechanism. Some aspects of the Model mean state are validated from available observations, which justifies a vertical Mode decomposition of the Model variability. The analysis of the Baroclinic Mode contributions to sea level indicates that the gravest Mode is dominant over most of the domain at all frequencies. Annual variability is on average twice as large as the semi-annual variability which is confined near the coast for all the Modes. The first Baroclinic Mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude. The higher-order Modes only contribute near the coast where they are associated with vertically propagating energy. The residual variability, which is the energy at all timescales other than annual and semi-annual periods peaks offshore between similar to 20 degrees S and similar to 30 degrees S for all Baroclinic Modes. The third Baroclinic Mode also exhibits a relative maximum variability off the coast of Peru south of the critical latitude of the annual cycle (similar to 13 degrees S), where the Peru-Chile Undercurrent is the most intense. Sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non-linear interaction between annual Rossby waves and the mean flow, while the annual ETRWs in the Model result from the summed-contribution from both the local wind stress and remote equatorial forcing. Overall the study extends the classical analysis of sea level variability in the SEP based on linear theory, and suggests that the peculiarities of the Baroclinic Modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability. (C) 2008 Published by Elsevier Ltd

  • Vertical structure variability in a seasonal simulation of a medium-resolution regional Model of the Eastern South Pacific
    Progress in Oceanography, 2008
    Co-Authors: Boris Dewitte, Vincent Echevin, Marcel Ramos, Oscar Pizarro, Yves Du Penhoat
    Abstract:

    A seasonal simulation from a medium-resolution ocean general circulation Mode (OGCM) is used to investigate the vertical structure variability of the Southeast Pacific (SEP). The focus is on the extra-tropical Rossby wave (ETRW) variability and associated forcing mechanism. Some aspects of the Model mean state are validated from available observations, which justifies a vertical Mode decomposition of the Model variability. The analysis of the Baroclinic Mode contributions to sea level indicates that the gravest Mode is dominant over most of the domain at all frequencies. Annual variability is on average twice as large as the semi-annual variability which is confined near the coast for all the Modes. The first Baroclinic Mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude. The higher-order Modes only contribute near the coast where they are associated with vertically propagating energy. The residual variability, which is the energy at all timescales other than annual and semi-annual periods peaks offshore between similar to 20 degrees S and similar to 30 degrees S for all Baroclinic Modes. The third Baroclinic Mode also exhibits a relative maximum variability off the coast of Peru south of the critical latitude of the annual cycle (similar to 13 degrees S), where the Peru-Chile Undercurrent is the most intense. Sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non-linear interaction between annual Rossby waves and the mean flow, while the annual ETRWs in the Model result from the summed-contribution from both the local wind stress and remote equatorial forcing. Overall the study extends the classical analysis of sea level variability in the SEP based on linear theory, and suggests that the peculiarities of the Baroclinic Modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability. (C) 2008 Published by Elsevier Ltd.

  • Rectification of ENSO Variability by Interdecadal Changes in the Equatorial Background Mean State in a CGCM Simulation
    Journal of Climate, 2007
    Co-Authors: Boris Dewitte, Sang-wook Yeh, Carole Cibot, Byung-kwon Moon, Laurent Terray
    Abstract:

    The link between the changes in equatorial background stratification and El Nino-Southern Oscillation (ENSO) modulation is investigated using a simulation from a 260-yr-long coupled general circulation Model (CGCM). The work focuses on the role of nonlinearities associated with equatorial wave dynamics. As a first step, the low-frequency change in mean stratification is diagnosed and documented from the shallow-water parameters derived from a vertical Mode decomposition of the CGCM. The parameters vary differently according to the Baroclinic Mode order, which may explain why a flattening thermocline does not necessarily lead to reduced ENSO activity. Estimations of Baroclinic Mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the Baroclinic Modes as compared to the interannual variability. In particular, the high-order Modes associated with decadal variability have a more pronounced signature in the western Pacific, whereas that associated with interannual variability (i.e., ENSO) shows more energy in the eastern Pacific. In the light of the results of the CGCM vertical Mode decomposition, an intermediate coupled Model (ICM) is used to test whether the nonlinearities associated with the changes in the Baroclinic Mode energy distribution can lead to coherent ENSO modulation. The results indicate that rectification of the interannual variability (ENSO time scales) by the interdecadal variability associated with changes in the oceanic mean states takes place in the ICM. The rectified effect results mostly in an increased variability and skewness of the zonal advection, which tends to produce a zonal seesaw of the sea surface temperature anomaly. A tropical mechanism for producing ENSO modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal Mode of thermocline depth arising from Ekman-pumping anomalies located in the central South Pacific.

  • Rectification of the ENSO variability by interdecadal changes in the equatorial background mean state in a CGCM simulation
    Journal of Climate, 2007
    Co-Authors: Boris Dewitte, Sang-wook Yeh, Carole Cibot, Byung-kwon Moon, Laurent Terray
    Abstract:

    The link between the changes in equatorial background stratification and El Niño-Southern Oscillation (ENSO) modulation is investigated using a simulation from a 260-yr-long coupled general circulation Model (CGCM). The work focuses on the role of nonlinearities associated with equatorial wave dynamics. As a first step, the low-frequency change in mean stratification is diagnosed and documented from the shallow-water parameters derived from a vertical Mode decomposition of the CGCM. The parameters vary differently according to the Baroclinic Mode order, which may explain why a flattening thermocline does not necessarily lead to reduced ENSO activity. Estimations of Baroclinic Mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the Baroclinic Modes as compared to the interannual variability. In particular, the high-order Modes associated with decadal variability have a more pronounced signature in the western Pacific, whereas that associated with interannual variability (i.e., ENSO) shows more energy in the eastern Pacific. In the light of the results of the CGCM vertical Mode decomposition, an intermediate coupled Model (ICM) is used to test whether the nonlinearities associated with the changes in the Baroclinic Mode energy distribution can lead to coherent ENSO modulation. The results indicate that rectification of the interannual variability (ENSO time scales) by the interdecadal variability associated with changes in the oceanic mean states takes place in the ICM. The rectified effect results mostly in an increased variability and skewness of the zonal advection, which tends to produce a zonal seesaw of the sea surface temperature anomaly. A tropical mechanism for producing ENSO modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal Mode of thermocline depth arising from Ekman-pumping anomalies located in the central South Pacific.

  • RECTIFICATION OF THE ENSO VARIABILITY BY INTERDECADAL CHANGES IN THE EQUATORIAL BACKGROUND MEAN STATE IN A CGCM SIMULATION
    Gayana (Concepción), 2004
    Co-Authors: Boris Dewitte, Sang-wook Yeh, Carole Cibot, Laurent Terray
    Abstract:

    Abstract The link between the changes in equatorial background stratification and El Nino–Southern Oscillation (ENSO) modulation is investigated using a simulation from a 260-yr-long coupled general circulation Model (CGCM). The work focuses on the role of nonlinearities associated with equatorial wave dynamics. As a first step, the low-frequency change in mean stratification is diagnosed and documented from the shallow-water parameters derived from a vertical Mode decomposition of the CGCM. The parameters vary differently according to the Baroclinic Mode order, which may explain why a flattening thermocline does not necessarily lead to reduced ENSO activity. Estimations of Baroclinic Mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the Baroclinic Modes as compared to the interannual variability. In particular, the high-order Modes associated with decadal variability have a more pronounced signature in the western Pacific, whereas that associated...

Ke Huang - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics and mechanism of annual sea level variability in the southern tropical  Indian Ocean
    2021
    Co-Authors: Ke Huang
    Abstract:

    <p>The first Baroclinic Mode Rossby wave is known to be of critical importance to the annual sea level variability in the southern tropical Indian Ocean (STIO; 0°–20°S, 50°–115°E). In this study, an analysis of continuously stratified linear ocean Model reveals that the second Baroclinic Mode also has significant contribution to the annual sea level variability (as high as 81% of the first Baroclinic Mode). The contributions of residual high-order Modes (3 # n # 25) are much less. The superposition of low-order (first and second) Baroclinic Rossby waves (BRWs) primarily contribute to the high energy center of sea level variability at ;108S in the STIO and the vertical energy penetration below the seasonal thermocline. We have found that 1) the low-order BRWs, having longer zonal wavelengths and weaker damping, can couple more efficiently to the local large-scale wind forcing than the high-order Modes and 2) the zonal coherency of the Ekman pumping results in the latitudinal energy maximum of low-order BRWs. Overall, this study extends the traditional analysis to suggest the characteristics of the second Baroclinic Mode need to be taken into account in interpreting the annual variability in the STIO.</p>

  • Baroclinic Characteristics and Energetics of Annual Rossby Waves in the Southern Tropical Indian Ocean
    Journal of Physical Oceanography, 2020
    Co-Authors: Ke Huang, Dongxiao Wang, Ming Feng, Weiqing Han, Gengxin Chen, Chaojiao Sun, Xiaolin Zhang, Qiang Xie, Weiqiang Wang, Qinyan Liu
    Abstract:

    AbstractThe first Baroclinic Mode Rossby wave is known to be of critical importance to the annual sea level variability in the southern tropical Indian Ocean (STIO; 0°–20°S, 50°–115°E). In this study, an analysis of continuously stratified linear ocean Model reveals that the second Baroclinic Mode also has significant contribution to the annual sea level variability (as high as 81% of the first Baroclinic Mode). The contributions of residual high-order Modes (3 ≤ n ≤ 25) are much less. The superposition of low-order (first and second) Baroclinic Rossby waves (BRWs) primarily contribute to the high energy center of sea level variability at ~10°S in the STIO and the vertical energy penetration below the seasonal thermocline. We have found that 1) the low-order BRWs, having longer zonal wavelengths and weaker damping, can couple more efficiently to the local large-scale wind forcing than the high-order Modes and 2) the zonal coherency of the Ekman pumping results in the latitudinal energy maximum of low-order BRWs. Overall, this study extends the traditional analysis to suggest the characteristics of the second Baroclinic Mode need to be taken into account in interpreting the annual variability in the STIO.

  • Determination of Spatiotemporal Variability of the Indian Equatorial Intermediate Current
    Journal of Physical Oceanography, 2020
    Co-Authors: Gengxin Chen, Ke Huang, Weiqing Han, Xiaolin Zhang, Linlin Liang, Huijie Xue, Dongxiao Wang
    Abstract:

    AbstractUsing 4-yr mooring observations and ocean circulation Model experiments, this study characterizes the spatial and temporal variability of the Equatorial Intermediate Current (EIC; 200–1200 m) in the Indian Ocean and investigates the causes. The EIC is dominated by seasonal and intraseasonal variability, with interannual variability being weak. The seasonal component dominates the midbasin with a predominant semiannual period of ~166 days but weakens toward east and west where the EIC generally exhibits large intraseasonal variations. The resonant second and fourth Baroclinic Modes at the semiannual period make the largest contribution to the EIC, determining the overall EIC structures. The higher Baroclinic Modes, however, modify the EIC’s vertical structures, forming multiple cores during some time periods. The EIC intensity has an abrupt change near 73°E, which is strong to the east and weak to the west. Model simulation suggests that the abrupt change is caused primarily by the Maldives, which block the propagation of equatorial waves. The Maldives impede the equatorial Rossby waves, reducing the EIC’s standard deviation associated with reflected Rossby waves by ~48% and directly forced waves by 20%. Mode decomposition further demonstrates that the semiannual resonance amplitude of the second Baroclinic Mode reduces by 39% because of the Maldives. However, resonance amplitude of the four Baroclinic Mode is less affected, because the Maldives fall in the node region of Mode 4’s resonance. The research reveals the spatiotemporal variability of the poorly understood EIC, contributing to our understanding of equatorial wave–current dynamics.

  • features of the equatorial intermediate current associated with basin resonance in the indian ocean
    Journal of Physical Oceanography, 2018
    Co-Authors: Ke Huang, Dongxiao Wang, Weiqing Han, Qiang Xie, Weiqiang Wang, Ju Chen, Gengxin Chen
    Abstract:

    AbstractThis paper investigates the features of the Equatorial Intermediate Current (EIC) in the Indian Ocean and its relationship with basin resonance at the semiannual time scale by using in situ observations, reanalysis output, and a continuously stratified linear ocean Model (LOM). The observational results show that the EIC is characterized by prominent semiannual variations with velocity reversals and westward phase propagation and that it is strongly influenced by the pronounced second Baroclinic Mode structure but with identifiable vertical phase propagation. Similar behavior is found in the reanalysis data and LOM results. The simulation of wind-driven equatorial wave dynamics in the LOM reveals that the observed variability of the EIC can be largely explained by the equatorial basin resonance at the semiannual period, when the second Baroclinic Rossby wave reflected from the eastern boundary intensifies the directly forced equatorial Kelvin and Rossby waves in the basin interior. The sum of the ...

Roberto C Mechoso - One of the best experts on this subject based on the ideXlab platform.

  • Baroclinic to barotropic pathway in el nino southern oscillation teleconnections from the viewpoint of a barotropic rossby wave source
    Journal of the Atmospheric Sciences, 2016
    Co-Authors: Xuan Ji, David J Neelin, Roberto C Mechoso
    Abstract:

    AbstractThe Baroclinic-to-barotropic pathway in ENSO teleconnections is examined from the viewpoint of a barotropic Rossby wave source that results from decomposition into barotropic and Baroclinic components. Diagnoses using the NCEP–NCAR reanalysis are supplemented by analysis of the response of a tropical atmospheric Model of intermediate complexity to the NCEP–NCAR barotropic Rossby wave source. Among the three barotropic Rossby wave source contributions (shear advection, vertical advection, and surface drag), the leading contribution is from shear advection and, more specifically, the mean Baroclinic zonal wind advecting the anomalous Baroclinic zonal wind. Vertical advection is the smallest term, while surface drag tends to cancel and reinforce the shear advection in different regions through damping on the Baroclinic Mode, which spins up a barotropic response. There are also nontrivial impacts of transients in the barotropic wind response to ENSO. Both tropical and subtropical Baroclinic vorticity ...

  • el nino southern oscillation sea level pressure anomalies in the western pacific why are they there
    Journal of Climate, 2015
    Co-Authors: David J Neelin, Roberto C Mechoso
    Abstract:

    AbstractAlthough sea level pressure (SLP) anomalies in the western Pacific have long been recognized as an integral part of the classic Southern Oscillation pattern associated with El Nino–Southern Oscillation (ENSO), there is an unresolved question regarding the dynamics that maintain these anomalies. Traditional studies of the ENSO response in the tropics assume a single deep Baroclinic Mode associated with the tropospheric temperature anomalies. However, the SLP anomalies in the western Pacific are spatially separated from the Baroclinic signal in the NCEP–NCAR reanalysis, CMIP5 Models, and an intermediate complexity Model [a quasi-equilibrium tropical circulation Model (QTCM)]. Separation of ENSO SLP anomalies in the tropical Pacific into Baroclinic and barotropic components indicates that the barotropic component contributes throughout the tropics and constitutes the primary contribution in the western Pacific. To demonstrate the roles of Baroclinic and barotropic Modes in ENSO teleconnections within...

Yves Dupenhoat - One of the best experts on this subject based on the ideXlab platform.

  • Vertical structure variability in a seasonal simulation of a medium-resolution regional Model of the Eastern South Pacific
    Progress in Oceanography, 2008
    Co-Authors: Boris Dewitte, Vincent Echevin, Marcel Ramos, Oscar Pizarro, Yves Dupenhoat
    Abstract:

    0079-6611International audienceA seasonal simulation from a medium-resolution ocean general circulation Mode (OGCM) is used to investigate the vertical structure variability of the Southeast Pacific (SEP). The focus is on the extra-tropical Rossby wave (ETRW) variability and associated forcing mechanism. Some aspects of the Model mean state are validated from available observations, which justifies a vertical Mode decomposition of the Model variability. The analysis of the Baroclinic Mode contributions to sea level indicates that the gravest Mode is dominant over most of the domain at all frequencies. Annual variability is on average twice as large as the semi-annual variability which is confined near the coast for all the Modes. The first Baroclinic Mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude. The higher-order Modes only contribute near the coast where they are associated with vertically propagating energy. The residual variability, which is the energy at all timescales other than annual and semi-annual periods peaks offshore between similar to 20 degrees S and similar to 30 degrees S for all Baroclinic Modes. The third Baroclinic Mode also exhibits a relative maximum variability off the coast of Peru south of the critical latitude of the annual cycle (similar to 13 degrees S), where the Peru-Chile Undercurrent is the most intense. Sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non-linear interaction between annual Rossby waves and the mean flow, while the annual ETRWs in the Model result from the summed-contribution from both the local wind stress and remote equatorial forcing. Overall the study extends the classical analysis of sea level variability in the SEP based on linear theory, and suggests that the peculiarities of the Baroclinic Modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability. (C) 2008 Published by Elsevier Ltd

  • tropical pacific Baroclinic Mode contribution and associated long waves for the 1994 1999 period from an assimilation experiment with altimetric data
    Journal of Geophysical Research, 2003
    Co-Authors: Boris Dewitte, Serena Illig, Laurent Parent, Yves Dupenhoat, Lionel Gourdeau, Jacques Verron
    Abstract:

    [1] An Ocean General Circulation Model (OGCM) of the tropical Pacific in which combined TOPEX/Poseidon and ERS sea level anomalies are assimilated over January 1994 through July 1999, is used to investigate equatorial wave characteristics during the intense 1997–1999 El Nino-La Nina event. Near the equator, the linear vertical Modes are estimated at each grid point of the OGCM simulation with and without assimilation. Consistently with an increase of the vertical gradient within the thermocline and a rise of the thermocline depth in the eastern basin, the assimilation results in an increased contribution of the higher-order Baroclinic Modes in the eastern basin and a decreased contribution of the first Baroclinic Mode in the western Pacific for the zonal current variability. For pressure, the first Baroclinic Mode contribution is reduced whereas the higher-order Modes contribution is weakly impacted. Kelvin and first-meridional Rossby waves are then derived for the first two more energetic Baroclinic Modes in the simulation with assimilation. Kelvin waves of both Modes constructively contribute to the strong warming observed in 1997, with the first (second) Baroclinic Mode being more energetic than the second (first) Baroclinic Mode in the early (mature) stage of the warming. Kelvin waves of both Modes reflect as first meridional Rossby waves at the eastern boundary (reflection efficiency of ∼95%) and contribute to push back the warm pool westward. The reversal of the warming is apparently initiated by the second Baroclinic Mode contribution which controls the position of the 28°C isotherm in the surface layer in the far eastern Pacific from January 1998. At the western boundary, reflections of Rossby waves take place for both Modes with an estimated total efficiency of ∼50% at 165°E. This suggests that, in our Model, the delayed oscillator theory is not applicable for explaining the reversal from warm to cold conditions in 1998 while the zonal advective feedback was at work. More generally, the study suggests that it is necessary to take into account the vertical structure of the ocean when interpreting altimetric data, which can be done through an assimilation experiment.

  • On the importance of subsurface variability for ENSO simulation and prediction with intermediate coupled Models of the Tropical Pacific: A case study for the 1997–1998 El Niño
    Geophysical Research Letters, 2002
    Co-Authors: Boris Dewitte, Yves Dupenhoat, Dacha Gushchina, Sergey Lakeev
    Abstract:

    [1] Two intermediate ocean-atmosphere coupled Models of the tropical Pacific are used to investigate the sensitivity of the forecasts of the 1997–1998 El Nino to the configuration of the oceanic vertical structure. The Models consist in a three Baroclinic Mode tropical Pacific Ocean and differ from their atmospheric part which is either a Gill (1980)'s tropical atmosphere or a statistical atmosphere. Forced with observed winds, the ocean Model simulates dynamical fields in better agreement with observations compared to a single Baroclinic Mode Model. In forecasting sea surface temperature anomalies in the eastern Pacific, the Models are comparable to prediction systems of similar complexity. Results of sensitivity tests to the oceanic vertical structure indicate that the second and third Baroclinic Mode contributions are necessary to better capture the rise in SST anomalies from April 1997 along with the amplitude of the event at its mature phase.

Bo Qiu - One of the best experts on this subject based on the ideXlab platform.

  • Intraseasonal‐to‐semiannual variability of sea‐surface height in the astern, equatorial Indian Ocean and southern Bay of Bengal
    Journal of Geophysical Research: Oceans, 2017
    Co-Authors: Xuhua Cheng, Julian P. Mccreary, Bo Qiu
    Abstract:

    Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½−layer (first Baroclinic Mode) and linear, continuously stratified (LCS; multi-Baroclinic-Mode) Models. The amplitude and dominant period of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB, respectively. Along the Sumatran west coast, SSH variability peaks at 30 − 60 days, 90 days, and 180 days. Along 5°N and east of Sri Lanka, the 30 − 60-day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½−layer Model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30 − 60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 − 120-day energy into the intraseasonal band of 30 − 60 days. The LCS solutions show that the first two Baroclinic Modes explain most of the SSH variance at 90 − 180 days. The second Baroclinic Mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.

  • intraseasonal to semiannual variability of sea surface height in the astern equatorial indian ocean and southern bay of bengal
    Journal of Geophysical Research, 2017
    Co-Authors: Xuhua Cheng, Julian P. Mccreary, Bo Qiu
    Abstract:

    Intraseasonal-to-semiannual variability of sea-surface height (SSH) in the eastern, equatorial Indian Ocean (EEIO) and southern Bay of Bengal (BoB) is investigated using altimetric data, and solutions to 1½−layer (first Baroclinic Mode) and linear, continuously stratified (LCS; multi-Baroclinic-Mode) Models. The amplitude and dominant period of SSH variability differ regionally. Large-amplitude variability is found along the west coast of Sumatra, in a zonal band across the BoB centered along 5°N, east of Sri Lanka, and in the northwestern BoB, respectively. Along the Sumatran west coast, SSH variability peaks at 30 − 60 days, 90 days, and 180 days. Along 5°N and east of Sri Lanka, the 30 − 60-day variability is dominant. Sensitivity experiments using a nonlinear version of the 1½−layer Model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern BoB. At 30 − 60 days, the solutions show that eddies (nonlinear Rossby waves) propagating from the east, rather than local wind forcing, account for most of the variance east of Sri Lanka; furthermore, they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 − 120-day energy into the intraseasonal band of 30 − 60 days. The LCS solutions show that the first two Baroclinic Modes explain most of the SSH variance at 90 − 180 days. The second Baroclinic Mode dominates the SSH variance at 180 days, a consequence of basin resonance and strong wind forcing.